As one of the methods for joining metal members with each other, friction welding has been proposed. “Friction welding” is the method of bringing the joining surfaces of the metal members to be joined into contact with each other and applying pressure to the joining surfaces while mechanically making them move relative to each other to generate heat of friction and using this as the heat source for pressure welding. The relative motion of the members includes, for example, rotational motion about the axis vertical to the contacting surfaces, back and forth motion in a direction parallel to the contacting surfaces, etc. Friction welding does not utilize ohmic heating, so large power facilities are not required and relatively simple facilities can be used to obtain products with a high dimensional precision. Due to this, the method is applied for joining parts which have been subjected to finishing processes. Further, unlike general welding, different types of metal materials can also be joined, so the fields of application are broad. For this reason, this is being applied to valves for automobiles and other numerous precision machine parts etc.
Friction welding requires heating up to close to the melting point of the metal members and bonding by plastic flow near the joining surfaces. For this reason, deformation easily occurs near the joining surfaces. Further, the heat affected zone of the metal members becomes wider. That has a detrimental effect in terms of the strength and material characteristics. For this reason, various methods have been proposed as methods for controlling the heat affect of the metal members.
PLT 1 discloses a method of joining metal members with different heat capacities by friction welding during which inserting an insert material as a rotating member between the metal members, individually controlling the two members in temperature, and making the insert material rotate for frictional joining. In the friction welding method of PLT 1, the pair of metal members can be joined through the insert member.
PLT 2 proposes to lower the joining temperature by joining an amorphous alloy foil (solder material for soldering) used for liquid phase diffusion bonding to a metal member in advance by the friction welding method. That is, the primary joining of the friction welding can be performed at a temperature of the melting point of the soldering material (amorphous metal foil) or less and the secondary joining of the liquid phase diffusion bonding (soldering) can be performed at a temperature of the extent of the melting point of the soldering material (amorphous metal foil). For this reason, compared with the usual friction welding, the temperature can be lowered, so there is little deformation and the heat affected zone of the metal members can be made smaller. However, the method of PLT 2 basically joins metal members by liquid phase diffusion bonding, not friction welding.